1. Field of the Invention
This invention relates to flexible liners for use in shipment and storage of bulk materials in shipping containers which are used in vessels, trucks, trains, and other means of moving containers. The containers herein referred to are generally rectangular containers of the standard size which can be easily loaded and stacked on the various means for moving them in commerce and for storage. These containers have flexible liners installed in them which substantially conform to the shape of the generally rectangular or square container to receive the bulk cargo. In some cases the liners used in shipping containers are also known as “bulkhead” or “safety sheets” which generally do not line the whole container but line parts of a container such as two sidewalls, a floor and an end face/back panel which corresponds to the shipping container door and are placed in a container at its door end prior to filling. Bulk cargo includes such items or substances as forms of powder, pellets, flakes, granules and may include certain forms of liquid. Common examples of bulk cargo are coffee beans, plastic pellets, grains, and the like.
2. Description of Related Art
The use of flexible liners for installation in a standard international container for use in cargo vessels, trucks, railcars, and storage spaces are well known and they are designed to be inserted within the generally rectangular container and substantially conform to the shape of the rectangular container whether completely lining the container or conforming to only a portion of the container such as with “bulkhead” or “safety sheets”. These liners substantially cover the inside of the cargo vessel container for receiving the bulk materials and therefore the stored bulk materials inside the liner do not come in contact with the container walls or floor in one case and in the other cases only contact the container walls uncovered by the liners referred to as “bulkhead” or “safety sheets”.
The container liners of the prior art have come in two general types, whether full liners or “bulkhead” or “safety sheets”. The two types being those using metal support bars which are positioned across the end face or back panel which corresponds with the container doors and placed in the channel edges of the container door to secure the liner and those using various strap configuration which are attached to the container to hold the liner in the container for loading and unloading bulk cargo.
The problem with strap configurations in the prior art is that the 4 corner eye-latches in the corners of containers are not always located based on industry standards as to position of the eye-latches in the container and therefore relying on these anchoring points to tension straps and secure bars to make these system work was unpredictable relative to the performance of the prior art type flexible apparatus. Additionally, attempting to restrain the bulkhead bulging with a multitude of straps, often in the form of a net, incurs in substantial installation time of the liner inside of the container.
Also the prior art did not recognize and allocate material and reinforcement to the positions of the back panel where the greatest hydrostatic pressures occurred in the middle and lower sections of the back panel. The prior art simply tried to reinforce the back panel by providing holding straps and other rigid means for retaining the back strap against bulging.
The flexible container liners of the prior art may, even after being secured within the container, have its end panel, which corresponds to the doors of the shipping container, bulge out outwardly into the doorway opening of the container, when filling of a container with bulk product occurs. The bulging of the end panel of the liner is caused, because of the hydrostatic head created by the bulk product against the back panel. The bulging outwardly of the back panel into the doorway may obstruct the closing of the door of the container. Also bulk product cargos have a tendency to move about during shipment and can put greater hydrostatic head pressure on the back panel causing it to instantaneously bulge outwardly at the opening of the back doors of the container upon opening the container at its destination. This outward instantaneous bulging at the opening of the back doors of the container can be dangerous to stevedores or dockhands by driving the doors into them. Also, this instantaneous outward bulging can be a problem for containers which must be opened for inspection before reaching their final destination because the bulging out can prevent the doors of the container from being reclosed after cargo inspection or custom clearance.
In many cases the prior art using barless liners had to have additional safety bars, for a safety feature, to be used across the back panel for tilting discharge of the cargo, but many times the flexible containers had bulged so far outward that the metal bars could not be inserted across the back panels and locked in the channels on the inside of the doors to the container which prevented the use of the safety bars on tilting discharges.
The ability to control the hydrostatic head of the bulk product which causes bulging outward of the back panel is further compounded by the need for loading and discharge ports being located in the back panel to facilitate the loading and unloading of bulk materials into the liner positioned in the container. The loading and discharge ports must be clear and open to receive and discharge the bulk product without interfering with the bulk product flow in and out of the liner. Further, the loading and discharge ports must be clear of metal support bars or the various strap configurations which are used to attach the liner to the container to allow free outflow of bulk product. Also, some unloading procedures, such as tilting discharge, of containers further increase hydrostatic head against the back panel when the whole container and liner are tilted upward from the end opposite the container doors and the back panel to discharge the bulk product.
Various configurations of metal bar support members being placed across the back panel and various strap systems across the back panel and down the respective sides of the container liner have been used to attempt to control the hydrostatic head of the bulk product against bulging the back panel outward into the doorway of the container when the doors are open have proved from a safety perspective to be ineffective or expensive to install.
Also various strap systems have been used which are anchored to the back panel at one end and anchored at the other end to the floor panel or sidewall panels of the container liner, which is secured to the container, to attempt to secure the back panel against the effects of the hydrostatic head of the bulk product from bulging out the back panel into the doorway. The strap systems have been designed for maximum force pull back and to hold the back panel from bulging forward into the doorway by using strap angles of 60° or greater with the back panel to achieve as much holding force or pulling back force vectors as possible between the strap anchored to the back panel and the other strap end secured to the floor or either end of the liner. The prior art used strap holding force not hydrostatic forces applied to the straps to help hold the bulging forces in check. Also the restraining force of a strap is limited to the surface area of the strap itself (typically no more than 2″ in width), and therefore significant bulging still occurs in between straps.
Yet another problem as those skilled in the art will recognize is that the bulk product must be free to flow both into and out of the liner which is mounted in the container during loading and discharging of the bulk product. However if product is free to flow into and out of the liner, then it is free to flow during shipment which can cause a very large buildup of bulk product at the back panel with a corresponding high hydrostatic head against the back panel upon container's arrival at its destination. This negative tendency of shifting and stacking of bulk products causes increased hydrostatic head on the back panel which can be further enhanced when a tilting discharge of the container is required. A tilting discharge means that the container with this liner inside is tilted upward on its end away from its back panel to allow gravity to cause the bulk product to flow toward the back panel for discharge of the bulk product, but increases the hydrostatic head on the back panel which can cause it to fail causing uncontrolled release of the bulk product.
Baffles have been used within the liners to control the bulk product flow within the liners during shipment but these have tended to also be at steep angles such as toward 90° with the back panel so as not to interfere with the bulk product loading or discharge. The use of steep angles toward 90° were also used to give the baffles greater holding back effects on the back panels but effectively created separate compartments which are run lengthwise of the liner in the container. Because the baffles created separate compartments which are run lengthwise of the liner in the container, the bulk product in the separate compartments did not control the hydrostatic head of the bulk product against the back panel for control of the back panel's outward bulging through the doorway of the container. Not only were these lengthwise panels too intrusive in the loading space of the container, but also they did not stay in their position once the bulk product was loaded, as the bulk product inside of the container tried to distribute itself within this loading space, and encountered these barriers, that ultimately were forced out of position due to their flexible fabric material.